What is PCB aluminum substratePosted on 2020-01-03
What is PCB aluminum substrate
PCB aluminum substrate is a unique metal-based copper-clad board. PCB aluminum substrate has good thermal conductivity, electrical insulation performance and machining performance.
Characteristics of aluminum substrate
● Surface mount technology (SMT) for PCB aluminum substrate surface; PCB aluminum substrate has good heat dissipation operation in the circuit design scheme;
● PCB aluminum substrate can reduce temperature, improve product power density and reliability, and extend product life;
● PCB aluminum substrate can reduce the size and reduce hardware and assembly costs;
● PCB aluminum substrate can replace ceramic substrate for better mechanical endurance.
Structure of PCB aluminum substrate
PCB aluminum-based copper clad board is a metal circuit board material consisting of copper foil, thermally conductive insulation layer and metal substrate. Its structure is divided into three layers:
Circuit layer: It is equivalent to the copper-clad board of ordinary PCB.
Insulation layer: The insulation layer is a layer of low thermal resistance thermally conductive insulating material. Thickness: 0.003 “to 0.006” inches is the core calculation method of aluminum-based copper clad laminates and has been UL recognized.
Base layer: It is a metal substrate, usually aluminum or copper. Aluminum-based copper clad laminates and traditional epoxy glass cloth laminates.
The PCB aluminum substrate is composed of a circuit layer, a thermally conductive insulating layer, and a metal base layer; the circuit layer (ie, copper foil) is usually etched to form a printed circuit to connect the various components of the component to each other. In general, the circuit layer requires a large current carrying capacity. Capacity, so thicker copper foil should be used, and the thickness is generally 35μm ~ 280μm;
The thermal insulation layer is the core technology of PCB aluminum substrate. It is generally composed of a special polymer filled with special ceramics. It has low thermal resistance, excellent viscoelasticity, and has the ability to resist thermal aging. It can withstand mechanical and thermal stress. IMS-H01, IMS-H02, LED-0601 and other high-performance PCB aluminum substrates use this technology to make them have excellent thermal conductivity and high-strength electrical insulation properties;
The metal base layer is a supporting member of an aluminum substrate, which requires high thermal conductivity. Generally, it is an aluminum plate, and a copper plate (where the copper plate can provide better thermal conductivity) is suitable for conventional machining such as drilling, punching and cutting. PCB materials have incomparable advantages compared to other materials. Suitable for surface mount SMT technology of power components. No heat sink is needed, the volume is greatly reduced, the heat dissipation effect is excellent, and the good insulation performance and mechanical performance.
PCB aluminum substrate use
1. Audio equipment: input, output amplifier, balanced amplifier, audio amplifier, preamplifier, power amplifier, etc.
2. Power supply equipment: switching regulator `DC / AC converter` SW regulator, etc.
3. Communication electronic equipment: high-frequency amplifier `filter electrical appliances` reporting circuit.
4. Office automation equipment: motor driver, etc.
5. Automobile: electronic regulator `igniter` power controller, etc.
6. Computer: CPU board `floppy disk drive` power supply unit, etc.
7. Power module: converter `solid relay` rectifier bridge, etc.
what is the impedance board
The name of the impedance board is believed that many friends who are engaged in circuit boards are not unfamiliar. Then what exactly is an impedance board and what does an impedance board do? This has asked many friends who are engaged in circuit boards. Today we will learn what impedance is. board? What are the characteristics of the impedance board? The definition of an impedance plate is: a good laminated structure can control the characteristic impedance of a printed circuit board. Its wiring can form an easily controllable and predictable transmission line structure called an impedance plate.
1, impedance characteristic of printed circuit board
According to the theory of signal transmission, the signal is a function of time and distance variables, so every part of the signal on the connection may change. Therefore, determine the AC impedance of the connection, that is, the ratio of the change in voltage to the change in current is the characteristic impedance of the transmission line (Characteristic Impedance): The characteristic impedance of the transmission line is only related to the characteristics of the signal connection itself. In actual circuits, the resistance value of the wire itself is less than the distributed impedance of the system, which is like a high-frequency circuit. The characteristic impedance mainly depends on the distributed impedance of the unit distributed capacitance and unit distributed inductance of the connection. The characteristic impedance of an ideal transmission line depends only on the unit distributed capacitance and unit distributed inductance of the connection.
2, Calculation of printed circuit board characteristic impedance
The proportional relationship between the rising time of the signal and the time required for the signal to reach the receiving end determines whether the signal connection is considered a transmission line. The specific proportional relationship can be explained by the following formula: If the length of the wire connection of the PCB board is greater than 1 / b, the connection wire between the signals can be regarded as a transmission line. From the signal equivalent impedance calculation formula, it can be known that the impedance of the transmission line can be expressed by the following formula: at high frequencies (tens of megahertz to hundreds of megahertz), wL >> R is satisfied (of course, if the signal frequency is greater than 109Hz, then Considering the skin effect of the signal, this relationship needs to be studied carefully). Then for a certain transmission line, its characteristic impedance is a constant. The signal reflection phenomenon is caused by the inconsistency between the characteristic impedance of the driving end of the signal and the transmission line, and the impedance of the receiving end. For a CMOS circuit, the output impedance of the driving end of the signal is relatively small, being several tens of ohms. The input impedance at the receiving end is relatively large.
3. Characteristic impedance control of printed circuit board
The characteristic impedance of the conductor on the printed circuit board is an important indicator of circuit design, especially in the PCB design of high-frequency circuits, it must be considered whether the characteristic impedance of the conductor is consistent with the characteristic impedance required by the device or signal, and whether they match. Therefore, there are two concepts that must be paid attention to in the reliability design of PCB design.
4. Impedance control of printed circuit board
There are various signal transmissions in the conductors of the circuit board. When the frequency must be increased in order to increase its transmission rate, if the line itself is different due to factors such as etching, stack thickness, and wire width, it will cause the impedance to change, making it worthwhile. Signal is distorted. Therefore, the impedance of a conductor on a high-speed circuit board should be controlled within a certain range, which is called “impedance control”. The factors that affect the impedance of PCB traces are mainly the width of the copper wire, the thickness of the copper wire, the dielectric constant of the dielectric, the thickness of the dielectric, the thickness of the pad, the path of the ground wire, and the traces around the trace. Therefore, when designing the PCB, it is necessary to control the impedance of the wiring on the board to avoid signal reflection and other electromagnetic interference and signal integrity issues as much as possible to ensure the stability of the actual use of the PCB. The calculation method of the impedance of microstrip and stripline on the PCB can refer to the corresponding empirical formula.
Printed circuit board impedance matching In the circuit board, if there is a signal transmission, it is hoped that from the transmitting end of the power supply, it can be smoothly transmitted to the receiving end with the minimum energy loss, and the receiving end completely absorbs it without making any changes. Any reflection. To achieve this kind of transmission, the impedance in the line must be equal to the impedance inside the transmitting end. This is called “impedance matching”. When designing high-speed PCB circuits, impedance matching is one of the design elements. The impedance value has an absolute relationship with the wiring method. For example, whether to walk on the surface layer (Microstrip) or inner layer (Stripline / Double Stripline), the distance from the reference power layer or ground layer, trace width, PCB material, etc. will affect the characteristic impedance of the trace. In other words, the impedance value can only be determined after wiring, and the characteristic impedance produced by different PCB manufacturers also has slight differences. Generally, the simulation software cannot consider some impedance discontinuous wiring due to the limitation of the line model or the mathematical algorithm used. At this time, only some terminations, such as series resistance, can be reserved on the schematic diagram. Mitigates the effects of trace impedance discontinuities. The real solution to the problem is to try to avoid impedance discontinuities when wiring.
What is FPC flexible board
PCFPC is the abbreviation of Flexible Printed Circuit, also known as flexible circuit board, flexible printed circuit board, flexible circuit board, referred to as flexible board or FPC;
FPC flexible circuit board features: FPC flexible circuit board has the characteristics of high wiring density, light weight, thin thickness and so on. It can bend, fold and wind freely, and can move and expand freely in three-dimensional space. FPC flexible board has good heat dissipation performance, and F-PC can be used to reduce the volume. The FPC flexible board can achieve light weight, miniaturization, and thinness, thereby achieving integration of component devices and wire connections.
Use of FPC flexible circuit board
FPC flexible circuit boards use electronic products such as mobile phones, notebook computers, PDAs, digital cameras, and LCM. FPC flexible circuit board is a kind of highly reliable and excellent flexible printed circuit made of polyimide or polyester film as the substrate. According to the combination of the substrate and the copper foil, flexible circuit boards can be divided into two types: glued flexible boards and glueless flexible boards. Among them, the price of glue-free flexible board is much higher than that of glued flexible board, but its parameters such as flexibility, bonding force of copper foil and substrate, and flatness of pads are also better than glued flexible board. Therefore, it is generally only used in those places with high requirements; due to the high price of glued flexible boards, most of the flexible boards on the market are still glued flexible boards. Since the flexible board is mainly used in the occasions that need to be bent, if the design or process is not reasonable, it is easy to produce defects such as micro cracks and welding.
Structure of FPC flexible board
According to the number of layers, it is divided into single-layer boards, double-layer boards, and multilayer boards. The structure of a single-layer board is the simplest flexible board. Usually the base material + transparent glue + copper foil is a set of purchased raw materials, and the protective film + transparent glue is another purchased raw material. First, the copper foil is subjected to processes such as etching to obtain the required circuits, and the protective film is drilled to expose the corresponding pads. After cleaning, the two are combined by rolling. Then, the exposed pad portion is plated with gold or tin for protection. In this way, the big board is ready. Generally, a small circuit board is punched into a corresponding shape. There is also a solder resist layer printed directly on the copper foil without a protective film, so the cost will be lower, but the mechanical strength of the circuit board will be poor. Unless the strength is not high but the price needs to be as low as possible, it is best to apply a protective film.
The structure of the double-layer board is that when the circuit of the circuit is too complicated, the single-layer board cannot be wired, or copper foil is required for ground shielding, a double-layer board or even a multi-layer board is required. The most typical difference between a multilayer board and a single-layer board is the addition of a via structure to connect the copper foil layers. The first processing technology of general substrate + transparent glue + copper foil is to make vias. Drill holes in the substrate and copper foil first, and then plate a certain thickness of copper after cleaning, and the via holes will be completed. The subsequent manufacturing process is almost the same as the single-layer board.
FPC flexible board applications such as: MP3, MP4 player, portable CD player, home VCD, DVD, digital camera, mobile phone and mobile phone battery, medical, automotive fields Flexible copper clad laminate (FPC) based on epoxy resin!
Origin of the name FPC flexible board
Due to its special functions, it is used more and more widely, and is becoming an important variety of epoxy-based copper clad laminates. But our country started late and has to catch up. Epoxy flexible printed circuit boards have experienced more than 30 years of development since they achieved industrial production. From the 1970s ** into the real industrial mass production, until the late 1980s, due to the advent and application of a new class of polyimide film materials, flexible printed circuit boards made FPC non-sticky. FPC in a cemented form (generally referred to as “two-layer FPC”). In the 1990s, the development of photosensitive cover films corresponding to high-density circuits in the world led to a major change in FPC design. Due to the development of new application fields, the concept of its product form has undergone significant changes, which has been expanded to include a wider range of substrates for TAB and COB. The high-density FPC that emerged in the second half of the 1990s began to enter large-scale industrial production. Its circuit pattern is rapidly developing to a more subtle level, and the market demand for high-density FPCs is also growing rapidly; FPCs can also be called: flexible circuit boards; PCBs are called hard boards!
toplayer and bottomlayer: the top and bottom layers respectively, that is, the upper and lower layers of the external appearance of the circuit board, the usual signal lines are arranged on the top, such as double-layer boards. For multilayer boards, signal layer wiring can also be added in the middle.
Mechanical mechanical layer: defines the appearance of the entire PCB board, that is, the overall structure of the entire PCB board.
Keepoutlayer: A boundary defined on the copper side of the electrical characteristics of a cloth. That is to say, after the forbidden wiring layer is first defined, in the subsequent layout process, the lines with electrical characteristics cannot exceed the boundary of the forbidden wiring layer.
Bottomoverlay Bottom silkscreen layer: Defines the top and bottom silkscreen characters, which are the component numbers and some characters commonly seen on PCB boards.
Bottompaste: refers to the exposed copper and platinum that we can see.
Bottomsolder Bottom Solder Mask: In contrast to toppaste and bottompaste, it is a layer to cover green oil.
Drillguide via guide layer
Multiplayer: refers to all layers of the PCB
The line drawn by TopLayer is red, which is the upper layer of a normal double panel, which is not needed for a single panel.
The line drawn by BottomLayer (bottom layer) is blue, which is the layer of the line above the single panel.
MidLayer1 (Middle Layer 1) This is the first layer of the middle layer. It seems that there are 30 layers. Generally designers don’t use it. You don’t need to worry about it first, it is used in multi-panel. It is not displayed in 99SE by default and is not used.
MechanicalLayers (mechanical layer) (purple) is used to mark the size, and the board description is ignored when the PCB is copied, that is, the board is not visible when it is made, and the meaning of a simple point type comment.
TopOverlay (top silk screen layer) (yellow) is the character on the front of the board, which corresponds to the single layer of TopLayer (top layer).
BottomOverlay (bottom silkscreen layer) (brown) corresponds to BottomLayer (bottom layer), which is the character on the back of the board. The above two layers of characters are used when dual-panel.
KeepOutLayer (forbidden wiring layer) (purple with the same mechanical layer) is simply the board’s frame, appearance.